Many deadly pathogens are passed to humans from the animal kingdom. For example, monkeys are the sources of the type I human immunodeficiency virus (HIV-I), which causes acquired immune deficiency syndrome (AIDS) and monkeypox, which is similar to smallpox; ground-dwelling mammals are believed to be the source of the Ebola virus; fruit bats and pigs are the source of the Nipah virus; the Hendra virus comes from horses; the virus responsible for the “Hong Kong Flu” originated in chickens; and wild birds, especially ducks, are the sources of many of the deadly influenza viruses. Many diseases also have animal reservoirs. By way of example, mice carry Hanta virus, rats carry the Black Plague, and deer carry Lyme disease.